No brakes

I have an 83, ¾ ton, Chevy Suburban, 2 x 4 with 110000 miles. The brake light is on and when you press the pedal it goes almost to the floor with no pressure behind it and no brakes being applied. Upon pressing the pedal further the bakes begin to engage, but not that good. It has fluid, new brake pads and new calipers. I changed it all when the fluid ran low about 4 months ago and I had to bleed the lines and the bleeder valves broke on both sides, I think they were the original calipers. It has worked fine for the past 4 months. Than a week ago the pedal went almost to the floor and no brakes. I’m getting good vacuum on the booster but I’m just not sure if it is the booster or the master cylinder or something else that is bad. Any help is as always greatly appreciated and thank you in advance.